Syntactic polyolefin composition for pipe coating

ABSTRACT

The invention relates to a syntactic polyolefin composition for pipe coating, wherein the composition comprises a β-nucleated propylene polymer and microspheres. The invention also relates to a method for the preparation of the composition for pipe coating and to an off-shore pipe coated with the syntactic polyolefin composition.

FIELD OF THE INVENTION

The present invention relates to a syntactic polyolefin composition forpipe coating, to a method for the preparation thereof and to anoff-shore pipe coated with the syntactic polyolefin composition.

BACKGROUND OF THE INVENTION

Polyolefin coated pipes are used in off-shore applications for thetransportation of hot fluids, e.g. crude oil, and are often installed atthe sea-bottom, most often at depths of several hundred meters. Forthese applications steel pipes are preferred but also fibre reinforcedpipes, advanced multilayer pipe constructions made of metal and/orpolymer based layers, may be used. At these depths the temperature ofthe surrounding water is close to 0° C. which leads to extensive heatlosses from the transported fluid and significantly reduces flow orcauses blockage of the production lines. In order to efficiently pump,e. g. crude oil, it is required that the viscosity is sufficiently low,otherwise a higher pump efficiency or the installation of additionalheating units along the pipeline will be necessary.

To meet the insulation requirements on off-shore pipes it has previouslybeen suggested to coat the pipes with an insulating layer of so calledsyntactic polyolefins, i. e. composite polyolefin/filler materials inwhich the filler comprises hollow microspheres. As examples of thepolyolefin used mention may be made of e. g. linear low densitypolyethylene, blends of propylene polymers and olefin copolymerelastomers or syntactic polypropylene.

A disadvantage of such syntactic polyolefin coatings is the insufficientmechanical properties of pipes provided with such coatings. At thedepths in question the temperature difference between the surroundingwater, often having a temperature as low as 0° C., and the inside ofpipe, often having a temperature of 100-150° C., put high demands on themechanical properties. The water pressure on the coating is substantial,and without sufficient compression strength the insulating coating willbe compressed to a smaller thickness, thereby reducing its insulatingcapacity. Also, excellent mechanical properties are required for coatedpipes in order to avoid cracking of the coating during installationhandling and in service.

The term installation handling used herein means any installationtechnique such as coiling and uncoiling of the ready made pipelines,welding and other jointing techniques and on-shore or off-shoreinstallation, e. g. off-shore installation at the sea-bottom.Installation of coated pipes, in particular for off-shore applications,involves tough conditions for the protective coating layer, includinghigh stress, substantial elongation, surface damages, notches, impactevents, etc, both at low and high temperature conditions and at highhydrostatic pressure. The coating layer is not only protecting thepipeline as such, but is also doing so in a state of high stress and/orat elevated temperatures and pressures, making the coating mostsensitive to cracking, e. g. the stresses induced during coiling anduncoiling. During the service life of the coated pipeline, the coatinghas to protect the pipeline from damages and induced stress and crackformations at conditions close to 0° C., high hydrostatic pressureswhere a small damage or notch in the coating could propagate into alarge crack putting the pipeline as such at risk. With a high dynamicfracture toughness of the coating material no cracks will occur duringinstallation handling and in service.

Another problem is the difficulties in producing syntactic polyolefins.In particular, it is difficult to compound glass microspheres and otherhollow spherical fillers into a thermoplastic polymer matrix at lowenough shear forces to avoid crushing of the spheres during the process.Also, the thermal conductivity of an effective off-shore pipe insulationneeds to be low. When about 15% or more of the spheres in the matrix arecrushed, it is difficult to maintain the necessary low level of thermalconductivity. Furthermore, the structural properties of the syntacticpolyolefin are also adversely affected. This problem cannot be avoidedby adding a larger amount of microspheres since an excessive amount willcause additionally crushed microspheres due to higher forces involvedduring homogenisation, i. e. >15%, initiates cracks and furtherdeteriorates the mechanical properties.

European Patent Application no EP-A-473 215 discloses polyolefinsyntactic foams for pipeline insulation use, wherein microspheres thathave been treated with a chain scission agent are added to a fluidstream of short chain polypropylene or polybutylene to form a syntacticfoam insulative material. This method is taught as useful for producingmaterial of a low thermal conductivity. However, the plastic startingmaterials taught for use therein are generally not optimal for submarinepipe insulation, because while the short chain polypropylene orpolybutylene affords low breakage of the microspheres, the methodrequires the presence of a chain scission agent, coated on themicrospheres. The chain-scission agent is employed to cause a narrowingof the molecular weight distribution of the polyolefin. Without thepresence of this agent, the finished insulation would be unacceptablefor use as off-shore pipe insulation, because it would not behydrostatic pressure resistant, abuse resistant, or creep resistant.

SUMMARY OF THE INVENTION

The object of the invention is to provide a syntactic polyolefincomposition for pipe coating wherein the above mentioned drawbacks havebeen eliminated or alleviated.

Thus, it is an object of the present invention to provide a syntacticpolyolefin composition having superior thermal and mechanical propertieswhich may be prepared on a large scale on currently available equipment.

According to the present invention this object is achieved by asyntactic polyolefin composition for pipe coating, characterised in thatthe composition comprises a β-nucleated propylene polymer andmicrospheres, said composition having a melt flow rate (MFR₂; ISO 1133,condition D) at 230° C./2.16 kg in the range of 0.05-30 g/10 min and inthat the composition has an elongation at break of at least 3%.

A further object of the present invention is to provide a method for thepreparation of a syntactic polyolefin composition for pipe coating,characterised in that microspheres are evenly distributed by melt mixingin a composition comprising a β-nucleated propylene polymer and hollowmicrospheres, said composition having a melt flow rate at 230° C./2.16kg in the range of 0.05-30 g/10 min and in that the composition has anelongation at break of at least 3%.

Yet another object of the present invention is to provide an off-shorepipe coated with a syntactic polyolefin composition, characterised inthat it is coated with a composition according to any one of claims1-13.

By the syntactic polyolefin composition of the present invention it ispossible to achieve a pipe coating for off-shore installations havinglow thermal conductivity and excellent mechanical properties.

Other distinguishing features and advantages of the invention willappear from the following specification and the appended claims.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

A characterising feature of the composition of the present invention isthe presence of a β-nucleated propylene polymer. β-nucleated propylenepolymers are isotactic propylene polymers composed of chains in a 3₁helical conformation having an internal microstructure of β-formspherulites being composed of radial arrays of parallel stackedlamellae. This microstructure can be realized by the addition ofβ-nucleating agents to the melt and subsequent crystallization. Thepresence of the β-form can be detected through the use of wide angleX-ray diffraction (Moore, J., Polypropylene Handbook, p 134-135, HanserPublishers Munich, 1996).

In a preferred embodiment of the present invention the β-nucleatedpropylene polymer is a (co)polymer (i. e. a homopolymer or copolymer),characterised in that the β-nucleated propylene polymer is a (co)polymerwhich comprises at least 90.0 weight % of propylene and up to 10.0weight % of α-olefins with 2 or 4 to 18 carbon atoms, and that thepropylene polymer has a melt flow rate of 0.1-8 g/10 min at 230° C./2.16kg.

According to a more preferred embodiment of the present invention theβ-nucleated propylene polymer is a β-nucleated propylene block copolymerwith 90.0 to 99.9 weight % of propylene and 0.1 to 10.0 weight % ofα-olefins with 2 or 4 to 18 carbon atoms with a melt flow rate (MFR) of0.1 to 40 g/10 min at 230° C./2.16 kg, preferably 0.1 to 8 g/10 min at230° C./2.16 kg, whereby a test polyolefin pipe prepared from theβ-nucleated propylene copolymer has a critical pressure of >25 bars anda dynamic fracture toughness of >3.5 MNm^(−3/2) in the hydrostatic smallscale steady state (hydrostatic S₄) test at 3° C.

The method of determining the dynamic fracture toughness is disclosed inPlastics, Rubber and Composites Processing and Applications, Vol. 26,No. 9, pp. 387 ff.

According to another advantageous embodiment, the β-nucleated propylenepolymer is a β-nucleated propylene block copolymer having anIR_(τ)>0.98, a tensile modulus of ≧1100 MPa at 23° C. and a Charpyimpact strength, notched, of ≧6 kJ/m² at −20° C. The IR_(τ) of thepropylene polymer is measured by Infrared spectroscopy and calculated asdescribed in EP 0 277 514 A2, page 3.

The β-nucleated propylene polymer in the composition according to thepresent invention preferably has a melt flow rate of 0.1-70 g/10 min,more preferably 0.15-50 g/10 min, and most preferably 0.2-30 g/10 min at230° C./2.16 kg.

According to a further preferred embodiment the β-nucleated propylenepolymer has a tensile modulus of preferably ≧1300 MPa and mostpreferably ≧1500 MPa at 23° C.

Charpy impact strength of the β-nucleated propylene polymer ispreferably ≧6 kJ/m² at −20° C., more preferably ≧9 kJ/m² at −20° C.,most preferably ≧10 kJ/m² at −20° C.

According to a further embodiment, the β-nucleated propylene polymersare propylene copolymers obtained by polymerization with a Ziegler-Nattacatalyst system comprising titanium-containing solid components, anorganoalumina, magnesium or titanium compound as cocatalyst and anexternal donor according to the formulaR_(x)R′_(y)Si(MeO)_(4-x-y),wherein R and R′ are identical or different and are branched or cyclicaliphatic or aromatic hydrocarbon residues, and y and x independentlyfrom each other are 0 or 1, provided that x+y are 1 or 2.

A preferred external donor in the Ziegler-Natta catalyst system forproducing the β-nucleated propylene block copolymers isdicyclopentyldimethoxysilane.

According to an advantageous embodiment the β-nucleated propylenecopolymers contain 0,0001 to 2,0 wt %, based on the propylene copolymersused, of

-   -   dicarboxylic acid derivative type diamide compounds from        C₅-C₈-cycloalkyl monoamines or C₆-C₁₂-aromatic monoamines and        C₅-C₈-aliphatic, C₅-C₈-cycloaliphatic or C₆-C₁₂-aromatic        dicarboxylic acids, and/or    -   diamine derivative type diamide compounds from C₅-C₈-cycloalkyl        monocarboxylic acids or C₆-C₁₂-aromatic monocarboxylic acids and        C₅-C₈-cycloaliphatic or C₆-C₁₂ aromatic diamines, and/or    -   amino acid derivative type diamide compounds from amidation        reaction of C₅-C₈-alkyl-, C₅-C₈-cycloalkyl- or C₆-C₁₂-arylamino        acids, C₅-C₈-alkyl-, C₅-C₈-cycloalkyl- or C₆-C₁₂-aromatic        monocarboxylic acid chlorides and C₅-C₈-alkyl-,        C₅-C₈-cycloalkyl- or C₆-C₁₂-aromatic mono-amines, and/or    -   quinacridone derivative compounds of the type quinacridone        compounds, quinacridone-quinone compounds, and/or        dihydroquinacridone type compounds, and/or    -   dicarboxylic acid salts of metals from group IIa of periodic        system and/or mixtures of dicarboxylic acids and metals from        group IIa of periodic system, and/or    -   salts of metals from group IIa of periodic system and imido        acids of the formula        wherein x=1 to 4; R=H, —COOH, C₁-C₁₂-alkyl, C₅-C₈-cycloalkyl or        C₆-C₁₂-aryl, and Y=C₁-C₁₂-alkyl, C₅-C₈-cycloalkyl or C₆-C₁₂-aryl        -substituted bivalent C₆-C₁₂-aromatic residues,        as β-nucleating agent.

Examples of the dicarboxylic acid derivative type diamide compounds fromC₅-C₈-cycloalkyl monoamines or C₆-C₁₂-aromatic monoamines andC₅-C₈-aliphatic, C₅-C₈-cycloaliphatic dicarboxylic acids, optionallycontained in the β-nucleated propylene copolymer, are

-   -   N,N′-di-C₅-C₈-cycloalkyl-2,6-naphtalene dicarboxamide compounds        such as N,N′-dicyclohexyl-2,6-naphtalene dicarboxamide and        N,N′-dicyclooctyl-2-6-naphtalene dicarboxamide,    -   N,N′-di-C₅-C₈-cycloalkyl-4,4-biphenyldicarboxamide compounds        such as N,N′-dicyclohexyl-4,4-biphenyldicarboxamide and        N,N′-dicyclopentyl-4,4-biphenyldicarboxamide,    -   N,N′-di-C₅-C₈-cycloalkyl-terephthalamide compounds such as        N,N′-dicyclohexylterephtalamide and        N,N′-dicyclopentylterephtalamide,    -   N,N′-di-C₅-C₈-cycloalkyl-1,4-cyclohexanedicarboxamide compounds        such as N,N′-dicyclo-hexyl-1,4-cyclohexanedicarboxamide and        N,N′-dicyclohexyl-1,4-cyclopentanedicarboxamide.

Examples of the diamine derivative type diamide compounds fromC₅-C₈-cycloalkyl mono-carboxylic acids or C₆-C₁₂-aromatic monocarboxylicacids and C₅-C₈-cycloaliphatic or C₆-C₁₂-aromatic diamines, optionallycontained in the β-nucleated propylene copolymer, are

-   -   N,N′-C₆-C₁₂-arylene-bis-benzamide compounds such as        N,N′-p-phenylene-bis-benzamide and        N,N′-1,5-naphtalene-bis-benzamide,    -   N,N′-C₅-C₈-cycloalkyl-bis-benzamide compounds such as        N,N′-1,4-cyclopentane-bis-benzamide and        N,N′-1,4-cyclohexane-bis-benzamide.    -   N,N′-p-C₆-C₁₂-arylene-bis-C₅-C₈-cycloalkylcarboxamide compounds        such as N,N′-1,5-naphtalene-bis-cyclohexanecarboxamide and        N,N′-1,4-phenylene-bis-cyclohexanecarboxamide.    -   N,N′-C₅-C₈-cycloalkyl-bis-cyclohexanecarboxamide compounds such        as N,N′-1,4-cyclopentane-bis-cyclohexanecarboxamide and        N,N′-1,4-cyclohexane-bis-cyclohexanecarboxamide.

Examples of the amino derivative type diamide compounds, optionallycontained in the β-nucleated propylene copolymer, areN-phenyl-5-(N-benzoylamino)pentaneamide and/orN-cyclohexyl-4-(N-cyclohexylcarbonylamino)benz-amide.

Examples of the quinacridone type compounds, optionally contained in theβ-nucleated propylene copolymer, are quinacridone, dimethylquinacridoneand/or dimethoxyquinacridone.

Examples of the quinacridonequinone type compounds, optionally containedin the β-nucleated propylene copolymer, are quinacridonequinone, a mixedcrystal of 5,12-di-hydro (2,3b)acridine-7,14-dione withquino(2,3b)acridine-6,7,13,14-(5H,12H)-tetrone as disclosed in EP-B 0177 961 and/or dimethoxyquinacridonequinone.

Examples of the dihydroquinacridone type compounds, optionally containedin the β-nucleated propylene copolymer, are dihydroquinacridone,dimethoxydihydroquinacridone and/or dibenzodihydroquinacridone.

Examples of the dicarboxylic acid salts of metals from group IIa ofperiodic system, optionally contained in the β-nucleated propylenecopolymer, are pimelic acid calcium salt and/or suberic acid calciumsalt.

Examples of salts of metals from group IIa of periodic system and imidoacids of the formula

optionally contained in the β-nucleated propylene copolymer, are thecalcium salts of phtaloylglycine, hexahydrophtaloylglycine,N-phtaloyl-alanine and/or N-4-methylphtaloylglycine.

According to the invention the β-nucleated propylene polymer is mixedwith microspheres, which may be made of various organic and inorganicmaterials, such as glass, epoxy resin, phenolic resin orurea-formaldehyde resin. The microspheres should be rigid, i. e.non-compressible, and should have a density of at most about 0.8 g/cm³,preferably at most about 0.4 g/cm³. The outer diameter of themicrospheres should be 1-500 μm, preferably 5-200 μm and preferably themicrospheres are hollow. A preferred material is an inorganic glass,preferably a silica based glass, or a polymer or ceramics, a rigid foamstructure, etc.

In the present invention the microspheres are preferably untreated, i.e. they do not need any pretreatment with chain scission agent in orderto achieve an even distribution of the microspheres and excellentmechanical properties. This is an advantage compared to the prior artsuch as EP-A-473 215 mentioned above.

The density of the composition of β-nucleated propylene polymer mixedwith hollow microspheres should preferably be 500-850 kg/m³ and morepreferably 600-800 kg/m³.

Preferably, the microspheres are present in the composition in an amountof from 10 to 50 weight %, preferably 15 to 35%, more preferably 20-30weight % of the composition.

In order to improve the distribution of microspheres within the polymermatrix, to reduce the amount of microspheres crushed during processing,and to improve the processability, the MFR of the β-nucleated propylenepolymer may be increased by the incorporation into the polymer matrix ofa polyolefin, having a MFR of 100-1500, preferably 400-1200 g/10 min at230° C./2.16 kg. The amount of polyolefin, e. g. polyethylene orpolypropylene should be 0-30 weight %, preferably 10-25 weight %.

The syntactic polyolefin composition of the present invention maycontain usual auxiliary materials, such as 0.01 to 2.5 wt % stabilizersand/or 0.01 to 1 wt % processing aids, and/or 0.1 to 1 wt % antistaticagents and/or 0.2 to 3 wt % pigments, in each case based on the polymersused.

As stabilizers, preferably mixtures of 0.01% to 0.6 wt % phenolicantioxidants, 0.01% to 0.6 wt % 3-arylbenzofuranones, 0.01% to 0.6 wt %processing stabilizers based on phosphites, 0.01% to 0.6 wt % hightemperature stabilizers based on disulfides and thioethers and/or 0.01%to 0.8 wt % sterically hindered amines (HALS), are suitable.

The melt flow rate (MFR), which is equivalent to the term “melt index”previously used, is an important property of the syntactic polyolefincomposition for pipe coating according to the invention. The MFR isdetermined according to ISO 1133 and is indicated in g/10 min. The MFRis an indication of the flowability, and hence the processability, ofthe polymer. The higher the melt flow rate, the lower the viscosity ofthe polymer composition. The MFR is determined at different loadingssuch as 2,16 kg (MFR₂; ISO 1133, condition D). In the present inventionthe composition has an MFR₂ in the range of 0.05-30 g/10 min at 230°C./2.16 kg, more preferably in the range of 0.5-10 g/10 min at 230°C./2.16 kg and most preferably in the range of 1.0-5 g/10 min.

Another important property of the syntactic polyolefin composition forpipe coating according to the invention is the elongation at break,which is determined according to ISO 527-2/5A, sample thickness 2 mm,100 mm/min, at ambient temperature of 23° C. The elongation at break isa measure of the flexibility of the material and consequently itsability to endure handling, such as coiling, reeling, etc without theformation of cracks. During coiling of the pipe the extension of theinsulating layer may be up to about 5%, which requires a sufficientlyductile material. According to the invention the composition has anelongation at break of at least 3%, preferably at least 5%, and morepreferably at least 10%.

The tensile modulus is a measurement of the rigidity of the material andits ability to withstand high water pressures. The tensile modulus ofthe composition should preferably be at least 1500 MPa determinedaccording to ISO 527-2/1B, sample thickness 4 mm, 1 mm/min, 23° C.

Another property indicating the ability of the composition to endurehigh water pressures is the compression strength determined according toASTM D 695. At the present invention this compression strength shouldpreferably be ≧10 MPa and more preferably ≧15 MPa.

As previously stated the thermal conductivity of an effective off-shorepipe insulation needs to be low in order to attain the desired low levelof thermal conductivity. According to the invention the compositionpreferably has a K-value of less than 0.20 W/m°K, preferably less than0.17 W/m°K.

The present invention also relates to a method for the preparation of asyntactic polyolefin composition for pipe coating, in which hollowmicrospheres are evenly distributed by melt mixing in a compositioncomprising a β-nucleated propylene polymer and hollow microspheres, saidcomposition having a melt flow rate at 230° C./2.16 kg in the range of0.05-30 g/10 min, more preferably in the range of 0.5-10 g/10 min andmost preferably in the range of 1.0-5 g/10 min, and in that thecomposition has an elongation at break of at least 3%, morepreferably >5%, and most preferably >10%.

The method is generally carried out in a compounding or extruder unit,preferably in a co-rotating or counter-rotating twin screw extruder, orin an internal mixer such as a Banbury type mixer or in a single screwextruder such as a Buss Co-kneader or in a conventional single screwextruder. Static mixers such as Kenics, Koch, etc can also be used inaddition to the compounding or extruder units mentioned in order toimprove the distribution of the microspheres in the polymer matrix.Pellets of β-nucleated propylene block (co)polymer and optionally apropylene homopolymer are fed into the extruder. When the polymer ismelted the hollow microspheres are added to the melted polymer, morepreferably at a melt temperature of 30° C. above the melt temperature ofthe polymer, most preferably 50° C. above the melt temperature of thepolymer in a ratio to achieve the desired K-value of the composition.The microspheres and polymer are mixed in the extruder until themicrospheres are evenly distributed in the molten polymer. The moltenand homogenised compound is then fed from the extruder and eitherpelletized for subsequent use or used directly to coat a pipe andprepare a syntactic polyolefin coated pipe according to the presentinvention. Direct coating of the pipes is preferred and includes boththe pipe coating process based on co-extrusion, i. e. coating thecomplete circumference at the same time or by extrusion of a tape orfilm wounded around the pipe in a continuous process.

As indicated above the off-shore pipe coated with a syntactic polyolefincomposition of the present invention is preferably prepared by extrudingthe syntactic polyolefin composition of the invention, e. g. inconnection with the preparation thereof by melt mixing onto the pipe.Such direct coating of the pipes in a continuous process has theadvantages that intermediate processing steps involving cooling,pelletizing and remelting may be omitted. In this way the toughtreatments of pelletizing and especially remelting in an extruder, whichnormally to a substantial extent is performed by friction forces, areavoided. The result of such treatments is inevitably a large amount ofcrushed microspheres with accompanying higher heat conductivity and lossin mechanical properties. The pipe may be pretreated by coating with anepoxy resin layer and an compatibilizing layer on the epoxy resin layerbefore the coating with the syntactic polyolefin composition. Thethickness of the coating preferably is at least about 1-100 mm, morepreferably 20-50 mm.

The present invention will now be illustrated by way of non-limitingexamples of preferred embodiments in order to further facilitate theunderstanding of the invention.

EXAMPLES

Preparation of a β-Nucleated Propylene Block Copolymer.

A mixture of 90 weight % of a propylene block copolymer, obtained bycombined bulk and gas phase polymerization using a Ziegler-Nattacatalyst system with dicyclopentyldimethoxysilane as external donor,having an ethylene content of 8.3 weight %, an IR_(τ) of the propylenehomopolymer block of 0.985 and a melt flow rate of 0.30 g/10 min at 230°C./2.16 kg, 10 weight % of a master batch comprising 99 parts by weightof a propylene block copolymer having an ethylene content of 8.3% byweight, an IR_(τ) of the propylene homopolymer block of 0.985 and a meltflow rate of 0.30 g/10 min at 230° C./2.16 kg, and 1 part by weightpimelic acid calcium salt, and 0.1 weight % calcium stearate, 0.1 weight% tetrakis[methylene(3,5-di-t-butyl-hydroxyhydrocinnamate)]methane and0.1 weight % tris-(2,4-di-t-butylphenyl)phosphite, based on the sum ofthe propylene polymers used, is melted in a twin screw extruder with atemperature profile of 100/145/185/210/220/225/225/225/220/200/185° C.,homogenized, discharged and pelletized. The resulting propylenecopolymer has a melt flow rate of 0.32 g/10 min at 230° C./2.16 kg, atensile modulus of 1290 MPa and a Charpy impact strength, using notchedtest specimens, of 39 kJ/m² at −20° C.

Physical Properties of Microspheres

The used miccrospheres were Scotchlite™ Glass Bubbles having a densitywithin the range of 0.35-0.41 g/cm³, measured in accordance with ASTMD284 (1976 edition) and a bulk density in the range of 0.19-0.28 g/cm³.Isostatic test pressure evaluation, at a test pressure of 38.5 MPa,calculated from the change in density of a sample (mixed with talc)after exposure to dry nitrogen, resulted in % of survival of at least80% and typically 90%. Floatation, % by bulk volume, was typically 94%.Test values were typical when material was sampled in accordance withASTM D2841 (1988 edition).

Example 1-3

Preparation of a Composition Comprising a β-Nucleated Propylene Polymer,a Propylene Homopolymer and Hollow Microspheres.

Pellets of β-nucleated propylene block copolymer having a MFR of 0.3g/10 min at 230° C./2.16 kg prepared as described above and pellets of apolypropylene homopolymer having a MFR of 400 g/10 min at 230° C./2.16kg, were fed into the first mixer inlet of a Buss Co-Kneader 100MDK/E-11L/D, i. e. a single screw mixer with a downstream dischargesingle screw extruder with a pelletizing unit cutting pellets in themolten stage and cooled via water. The mixer temperatures were set to200-240° C., from first inlet to outlet, screw temperature to 210° C.and the discharge extruder to around 230° C. The mixer screw RPM was170-190 rpm and the throughput 100-150 kg/h. Untreated microspheres, asspecified above, were fed into the molten polymer in the second mixerinlet downstream. The compositions of the composite material are setforth in Table 1. The composite material was extruded and pelletized.TABLE 1 Example 1 Example 2 Example 3 Weight % weight % Weight %Propylene block co- 58.10 48.10 polymer, MFR 0.3 Propylene block co-83.8 polymer MFR 4.0 Homopolypropylene, 15.00 20.00 MFR 450 β-nucleator1.2 1.2 1.2 Glass microspheres 25.00 30.00 15.00 Stabilizers 0.74 0.740.74

The resulting properties from plaques compression moulded at 220° C. arepresented in Table 2. TABLE 2 Property Example 1 Example 2 Example 3MFR₂ at 230° C./2.16 kg, 0.55 0.9 5.4 ISO 1133 Density, kg/m³ 690 650739 ISO 1183 K-value, W/m° K, 0.174 0.188 ASTM C177 Fraction of brokenmicro- 14 8 spheres, % Tensile stress at 6 12 12 yield, MPa, ISO 527Elongation at break, % 98 7.6 9.4 ISO 527 Tensile modulus, Pa, 1900 ISO527 Compression strength 17.8 at 5% compression, MPa, ASTM D695

From Table 2 it can be seen that the composition according to theinvention provides a composite material which is well suited forinsulating purposes, having a K-value of 0.174 W/m°K and a density of650-690 kg/m³. The mechanical properties of the composition areexcellent with a high elongation at break of 98% and a tensile modulusof 1900 MPa. The compounding of the β-nucleated propylene polymer of MFR0.3 g/10 min at 230° C./2.16 kg and the propylene homopolymer of MFR 400g/10 min at 230° C./2.16 kg results in a composition having a MFR of0.55-0.9 g/10 min at 230° C./2.16 kg, and thus makes it possible toincorporate the hollow microspheres into the composition without anysignificant breakage of the microspheres. These values correspond to thevalues attained in the ready made pipe coating, whereincompounding/homogenisation and pipe extrusion is performed in acontinuous step, i. e. without extrusion remelting which causes anadditional amount of crushed microspheres.

Example 4

In order to simulate a two step procedure, wherein melt compoundingand/or homogenisation and palletising and/or solidification isaccomplished in a first step and pipe extrusion including remelting in asubsequent second step, the pellets manufactured in example 1 wereextruded in a labextruder through a tape die having a cross section of30×2 mm. The labextruder was a standard screw compression screw with aRPM of 30, a screw length L/D of 30 and a screw diameter of 30 mm. Thecompression ratio was 1:3, the set temperature 220° C., and the melttemperature 225° C. The resulting properties from plaques made of thetapes by compression moulding at 220° C., are presented in Table 3.TABLE 3 Property Example 4 MFR₂ at 230° C./2.16 kg, 0.57 ISO 1133Density, kg/m³ 722 ISO 1183 K-value, W/m° K, 0.18 ASTM C177 Fraction ofbroken microspheres, % Tensile stress at 6 yield, MPa, ISO 527Elongation at break, % 79 ISO 527

From the resulting properties presented in Table 3 it can be concludedthat a second extrusion step including remelting by extrusion stillgives suitable values for the application, e. g. a K-value of 0.18 W/m°Kand an elongation at break of 79%.

Comparative Examples 5 and 6

Pellets of propylene block copolymer were prepared as described abovefor examples 1-3. TABLE 4 Example 5 Example 6 Weight % weight %Propylene block co- 70 polymer, MFR 1.0 Propylene block co- 5 20 polymerMFR 8.0 Glass microspheres 25 20

The resulting properties from plaques compression moulded at 220° C. arepresented in Table 5. TABLE 5 Property Example 5 Example 6 MFR₂ at 230°C./2.16 kg, 0.38 2.5 ISO 1133 Density, kg/m³ 681 722 ISO 1183 Tensilestress at 8.7 13 yield, MPa, ISO 527 Elongation at break, % 0.1 2.2 ISO527

From the resulting properties presented in Table 5 it is evident thatcompositions without the addition of a β-nucleating agent have inferiormechanical properties in comparison to the compositions according to theinvention given in examples 1-4.

1. A syntactic polyolefin composition for pipe coating, wherein thecomposition comprises a β-nucleated propylene polymer comprising0.0001-2.0 weight % of a β-nucleating agent and microspheres, saidcomposition having a melt flow rate (MFR₂; ISO 1133, condition D) at230° C./2.16 kg in the range of 0.05-30 g/10 min and in that thecomposition has an elongation at break of at least 3%.
 2. A syntacticpolyolefin composition according to claim 1, wherein said compositionhas a melt flow rate (MFR₂; ISO 1133, condition D) at 230° C./2.16 kg inthe range of 0.5-10 g/10 min and preferably in the range of 1.0-5 g/10min.
 3. A syntactic polyolefin composition according to claim 1 whereinsaid composition has an elongation at break of >5% and preferably >10%.4. A syntactic polyolefin composition according to claim 1, wherein theβ-nucleated propylene polymer is a (co)polymer which comprises at least90.0 weight % of propylene and up to 10.0 weight % of α-olefins with 2or 4 to 18 carbon atoms, and that the propylene polymer has a melt flowrate of 0.1-8 g/10 min at 230° C./2.16 kg.
 5. A syntactic polyolefincomposition according to claim 1, wherein the composition furthercomprises a polyolefin homopolymer having a melt flow rate of 100-1500g/10 min at 230° C./2.16 kg.
 6. A syntactic polyolefin compositionaccording to claim 1, wherein the amount of polyolefin is 0-20 weight %,preferably 15-20 weight %.
 7. A syntactic polyolefin compositionaccording to claim 1, wherein the tensile modulus of the composition isat least 1500 MPa determined according to ISO
 527. 8. A syntacticpolyolefin composition according to claim 1, wherein the compressionstrength at 20 MPa/80° determined according to ASTM D695, is >10 MPa,preferably >15 MPa.
 9. A syntactic polyolefin composition according toclaim 1, wherein the K-value of the composition is less than 0.190W/m°K.
 10. A syntactic polyolefin composition according claim 1, whereinthe density of the composition is 500-850 kg/m3.
 11. A syntacticpolyolefin composition according to claim 1, wherein said microspheresare made of glass, ceramics, epoxy resin, phenolic resin orurea-formaldehyde resin.
 12. A syntactic polyolefin compositionaccording to claim 1, wherein said microspheres are untreatedmicrospheres.
 13. A syntactic polyolefin composition according to claim1, wherein said microspheres have an outer diameter of 1-500 μm,preferably 5-200 μm.
 14. A syntactic polyolefin composition according toclaim 1, wherein said microspheres are hollow.
 15. A syntacticpolyolefin composition according to claim 1, wherein said microspheresare present in an amount of 10-50 weight %, preferably 20-30 weight % ofthe composition.
 16. A method for the preparation of a syntacticpolyolefin composition for pipe coating according to claim 1, whereinmicrospheres are evenly distributed by melt mixing in a compositioncomprising a β-nucleated propylene polymer and microspheres, saidcomposition having a melt flow rate at 230° C./2.16 kg in the range0.05-30 g/10 min and in that the composition has an elongation at breakof at least 3%.
 17. A method according to claim 16, wherein saidmicrospheres are added to the molten polymer.
 18. A method according toclaim 16, wherein the composition is compounded/homogenised and extrudedas a coating on an off-shore pipe in one continuous step.
 19. A methodaccording to claim 16 or wherein, the composition is pelletized in afirst step and in a subsequent step extruded as a coating on anoff-shore pipe.
 20. An off-shore pipe coated with a syntactic polyolefincomposition, wherein the pipe is coated with a composition according toclaim 1.